1. Field of the Invention
The present invention relates to a single-wire asynchronous serial interface, in particular to a single-wire asynchronous serial interface which is capable of transmitting commands, data, and even power, and it is not required for the transmission side and the receiving side to synchronize their clocks.
2. Description of the Related Art
FIG. 1 shows a conventional arrangement for single-wire serial transmission between a transmitting side Tx and a receiving side Rx. The signals transmitted by the transmitting side Tx should include a start bit, a command of fixed bit length, data of fixed bit length, and a stop bit. The function of the start bit is for synchronization between the transmitting side Tx and the receiving side Rx; as shown by the arrow, when the receiving side Rx receives this start bit, it begins to generate clock signals in synchronization with the rising edge of the start bit. The receiving side Rx receives and counts the bit lengths of the command and the data according to the synchronous clock signals. The bit lengths of the command and the data should follow a protocol previously agreed between the transmitting side Tx and the receiving side Rx. Such a conventional arrangement is called “synchronous transmission” because the transmission side Tx and the receiving side Rx have to synchronize their clocks, and the transmitting side Tx has to transmit data according to the clock frequency of the receiving side Rx.
The above-mentioned conventional arrangement has the following drawbacks. First, the transmitting side Tx has to know the clock frequency of the receiving side Rx in advance. Second, to ensure correct receipt of command and data signals, the transmitting side Tx needs to properly arrange the set-up time and hold time of the transmitted signals. Furthermore, since the bit lengths of the command and data are fixed, there are only limited number of commands that can be transmitted. For example, if the bit length of a command signal is 5 bits, it can only transmit 25=32 types of commands.
FIG. 2 shows a conventional arrangement for single-wire tri-state data transmission, in which the transmitted data have three level states: 0, 1, or T (third-state). However, conventionally, such an arrangement is still for data transmission, except that there are three level states instead of two. No other use has been proposed.
In view of the foregoing drawbacks, the present invention proposes a single-wire asynchronous serial interface which is capable of transmitting commands, data, and even power, and it is not required for the transmission side and the receiving side to synchronize their clocks.